Concentrations and specific loads of brominated flame retardants in sewage sludge
Introduction
Polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCD) are high volume chemicals (HVC) which represent two important compound classes of brominated flame retardants (BFRs). PBDEs have been widely used to flame retard many everyday products such as furniture, cars, textiles and electronic equipment. DecaBDE, the main representative PBDE is added to plastics used in electrical and electronic equipment (housings of computers, TV sets, etc.), transportation sector (i.e., automotive interiors) and for construction and building (i.e., wires, cables, pipes, etc.). It is also employed as a flame retardant in textile back coating in furniture (BSEF, 2005a). HBCD’s main use is in expanded and extruded polystyrene for thermal insulation foams, in building and construction. Similar to decaBDE, HBCD is also applied in the backcoating of textiles, mainly for upholstery furniture. A very small application of HBCD is in high impact polystyrene, which is used for electrical and electronic appliances, for example in audio visual equipment (BSEF, 2005b). The amount added to the polymers might reach up to 18% for pentabrominated diphenyl ethers (pentaBDEs), 15% for octabrominated diphenyl ethers (octaBDEs) and 16% for decabrominated diphenyl ethers (decaBDEs) (Alaee et al., 2003) whilst percentages in products are varying between 0.8% and 4% for HBCD (Janak et al., 2005). The worldwide market demand in 2001 in metric tons (t) was reported to be 56 100 for decaBDE, 16 700 for HBCD, 7500 for pentaBDE and 3790 for octaBDE, respectively. The corresponding volumes for Europe were 9500 t for HBCD, 7600 t for decaBDE, 610 t for octaBDE and 150 t for pentaBDE, respectively. These figures make HBCD and decaBDE the second most used BFRs in Europe after tetrabromobisphenol A (TBBP-A). The worldwide market demand for HBCD and decaBDE was estimated to further increase through 2003 (BSEF, 2005c).
Some PBDEs exhibit physicochemical properties (environmental persistence, tendency to bioaccumulate) and potential toxicity that would categorize them as potential persistent organic pollutants (POPs) (Wania and Dugani, 2003). Penta- and octaBDEs are subject to bans in Europe since 2004 (BSEF, 2005c). HBCD might replace these compounds in some applications (Covaci et al., 2006). PBDEs and HBCD are both “additive” flame retardants being simply blended with the product, in contrast to “reactive” flame retardants (e.g., TBBP-A) that are covalently bound into the matrix (Morris et al., 2004). This may make them prone to release into the atmosphere. As a result of their widespread use, these BFRs are now considered ubiquitous in the environment. PBDEs and HBCD have been found in most environmental compartments, including air, soil, water, sediment, terrestrial and aquatic organisms and people (Law et al., 2003, Law et al., 2006, Hale et al., 2006).
As markets for products containing BFRs grow their widespread and increasing environmental occurrence is expected to double every 3–5 yr (Hites, 2004). Therefore, it seems reasonable to include these compounds into current monitoring programs. Sewage sludge represents an interesting matrix to observe time trends of hydrophobic compounds. It has been shown to contain many important organic pollutants and was considered as appropriate to characterize emissions of BFRs (Hale et al., 2002, Oeberg et al., 2002). However, data on BFRs in sewage sludge are still sparse (Hale et al., 2006). Lipophilic organic pollutants enter the wastewater stream after use in private households and industry or via aerial deposition on impervious surfaces and runoff into the sewage drains. During wastewater treatment, they preferentially partition onto solids and accumulate in sewage sludge (Langford et al., 2005). If the characteristics of the wastewater treatment plants (WWTPs) and their catchments are precisely described the sources of pollutants and trends for emissions can be characterized on the basis of sewage sludge. This topic has been followed within a network consisting of about 30 monitoring sites (WWTP and the corresponding catchment) in Switzerland for BFRs. The current study includes the following aims: (i) determination of the concentrations and the specific loads of BFRs in sewage sludge sampled in different types of monitoring sites and (ii) identification of their main sources.
Section snippets
Characterization of monitoring sites and sampling
The monitoring network comprises three types of sites which are appropriately characterized. Sites of type A include a separate sewer system and a rural catchment without industrial activities apart from a few craft industries. Sites B exhibit the same characteristics as type A but the catchment has a combined sewer system and some more craft industries. Sites of type C have a combined sewer system and an urban catchment including industry and craft industry. Out of the monitoring sites
Concentrations of BFRs in sewage sludge
The concentrations of BFRs determined in sewage sludge are shown in Table 1. The results are summarized as penta-, octa-, decaBDE and HBCD for discussion. PentaBDE was calculated according to the percentage of the sum of the main congeners BDE47, BDE99 and BDE100 in the technical mixture Bromkal 70-5DE and octaBDE according to the amount of BDE183 in Bromkal 79-8DE as determined by La Guardia et al. (2006). DecaBDE was assumed to correspond with the amount of BDE209. This simplification seems
Conclusions
Concentration levels and patterns of penta-, octa- and decaBDEs in sewage sludge are similar for Switzerland and other European countries. Sludge from Northern America comprise higher amounts of penta- and octaBDEs compared to samples of European origin which is in line with differences in consumption. The ratios between specific loads of penta-, octa-, decaBDE and HBCD can be explained by their consumption and the storage in the anthroposphere/environment, their potential for release from
Acknowledgements
This work was funded by the Swiss Agency for the Environment (SAE) and a pool of Swiss cantons (ZH, VD, BE, LU, BL and AG). P. Spohn and M. Blum (AWEL Zurich) are highly acknowledged for supplying a part of the sludge samples. We thank the personnel of the WWTPs for supplying data and for their collaboration in this project.
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